PROJECT 1 SUMMARY. Major depressive disorder (MDD) topped ischemic heart disease as the number one cause of disability worldwide, and women have twice the risk of men. Although this is well-known, even recent studies of brain circuitry and genes associated with mood dysregulation and MDD per se do not investigate sex effects nor incorporate even current sex-dependent knowledge into development of therapeutics. This is surprising since MDD is associated with abnormalities in stress response circuitry including hypothalamus (HYPO), amygdala (AMYG), hippocampus (HIPP), anterior cingulate cortex (ACC), and ventromedial and orbital prefrontal cortices (vmPFC, OFC), areas that are among the most sexually dimorphic in the brain. HIPP, HYPO, AMYG, and PFC are dense in sex steroid and glucocorticoid receptors coupled with cytokine receptors, in particular, TNF-?, IL-1?, IL-6, the major co-activators of the hypothalamic pituitary adrenal (HPA) axis. In fact, activity in these areas has been associated with cortisol response, autonomic dysfunction characterized by loss of parasympathetic cardiac tone, and immune responses, which we previously showed differed by sex. Furthermore, autonomic dysregulation is significantly associated with cardiovascular disease itself, with women at twice the risk of the co-occurrence of MDD and heart disease, leading to a 3-5-fold risk of death in women from heart disease, often with unrecognized and untreated MDD. This is a worldwide public health challenge, and thus understanding early biomarkers for the co-occurrence later in life will provide knowledge to intervene earlier. Leveraging a rare opportunity to investigate fetal antecedents to sex differences in adult MDD and associated impact on central and peripheral physiology in early midlife in human in vivo studies, we will test here that immune pathway abnormalities, beginning in fetal development, are associated with sex-dependent impacts on HYPO, HIPP, AMYG and PFC, resulting in lifelong recurrent MDD (rMDD), and dysregulation of hormone and immune responses to stress and autonomic dysfunction in early midlife. Adult subjects from our prenatal cohort, for whom prenatal sera are archived and who have been included in our follow-up studies for 60 years, will be re-recruited (80 cases with rMDD/50 healthy controls, equally divided by sex, now ages 55- 61) for the proposed study. We will test whether these prenatal immune biomarkers are associated with lifelong MDD and ANS and neurovascular dysregulation in early midlife (including structural and functional brain abnormalities in stress response circuitry, physiologic dysregulation) and neurovascular dysfunction. We predict that the sex differences in early midlife will be mediated by major depression in earlier adulthood, which we predict is associated with sex-selective dysregulation of innate immunity resulting from maternal prenatal exposure. Novel transcriptomic analyses of innate immunity genes will provide clues to immune pathways to sex differences in MDD and autonomic dysregulation. Our lifespan perspective is an innovative approach that will identify potential therapeutic sex-dependent targets for early intervention to attenuate disability later in life.